05. Single nanorod devices for battery diagnostics: A case study on LiMn2O4

This paper presents single nanostructure devices as a powerful new diagnostic tool for batteries with LiMn(2)O(4) nanorod materials as an example. LiMn(2)O(4) and Al-doped LiMn(2)O(4) nanorods were synthesized by a two-step method that combines hydrothermal synthesis of beta-MnO(2) nanorods and a solid state reaction to convert them to LiMn(2)O(4) nanorods. lambda-MnO(2) nanorods were also prepared by acid treatment of LiMn(2)O(4) nanorods. The effect of electrolyte etching on these LiMn(2)O(4)-related nanorods is investigated by both SEM and single-nanorod transport measurement, and this is the first time that the transport properties of this material have been studied at the level of an individual single-crystalline particle. Experiments show that Al dopants reduce the dissolution of Mn(3+) ions significantly and make the LiAl(0.1)Mn(1.9)O(4) nanorods much more stable than LiMn(2)O(4) against electrolyte etching, which is reflected by the magnification of both size shrinkage and conductance decrease. These results correlate well with the better cycling performance of Al-doped LiMn(2)O(4) in our Li-ion battery tests: LiAl(0.1)Mn(1.9)O(4) nanorods achieve 96% capacity retention after 100 cycles at 1C rate at room temperature, and 80% at 60 degrees C, whereas LiMn(2)O(4) shows worse retention of 91% at room temperature, and 69% at 60 degrees C. Moreover, temperature-dependent I-V measurements indicate that the sharp electronic resistance increase due to charge ordering transition at 290 K does not appear in our LiMn(2)O(4) nanorod samples, suggesting good battery performance at low temperature.